Many studies have demonstrated that women express stronger attraction to androgen-related traits when tested near ovulation than when tested at other times in the cycle. Much less research, however, has directly addressed which hormonal or other physiological signals may regulate these temporal shifts in women's attractiveness judgments. In the present study, we measured women's preferences for facial cues of men's testosterone concentrations on two occasions spaced two weeks apart, while also measuring women's salivary estradiol and testosterone concentrations at each testing session. Changes in women's estradiol concentrations across sessions positively predicted changes in their preferences for facial cues of high testosterone; there was no such effect for changes in women's testosterone concentrations. For the subset of women who had a testing session fall within the estimated fertile window, preferences for high testosterone faces were stronger in the fertile window session, and change in estradiol from outside to inside the fertile window positively predicted the magnitude of the ovulatory preference shift. These patterns were not replicated when testing preferences for faces that were rated as high in masculinity, suggesting that facial cues of high testosterone can be distinguished from the cues used to subjectively judge facial masculinity. Our findings suggest that women's estradiol promotes attraction to androgen-dependent cues in men (similar to its effects in females of various nonhuman species), and support a role for this hormone as a physiological regulator of cycle phase shifts in mating psychology. Copyright (c) 2010 Elsevier Ltd. All rights reserved.